In large vessels for storing and/or treating particulate material, such as wood chips, coal, metal ore, grain, etc., there is often a tendency for the particulate material to plug or channel, or for bridging of the particular material to occur, due to compression of the particulate material near the bottom of the vessel. Plugging or bridging can shut down entire industrial operations which rely upon the vessel as the source of supply of particulate material, and channeling can lead to improper treatment of the material, and inadequate turnover.
According to the present invention, a vessel for storing particulate material is provided which minimizes or substantially eliminates the pluggage or particulate bridging problems that have occurred in the past, and also minimizes the chances for channeling. This is accomplished according to the present invention by providing a particular surface configuration of the interior vertical wall of the vessel so as to reduce compression of particulates within the vessel. For example, for a chip bin having a height of wood chips within the bin of about 40 feet, and a bottom diameter of about 15 to 20 feet, the vertical solids pressure adjacent the bottom easily exceeds 400 psf. This pressure is so high that with some types of wood (e.g. cedar) it is almost certain to quickly result in pluggage or bridging, and with almost any type of wood chips there is a high probability that plugging or bridging will occur periodically. According to the invention, the vertical solids pressure is reduced so that the maximum within the vessel is about 250 psf, and preferably the vertical solids pressure is maintained at about 200 psf or less. This approximately one-half (or more) reduction in the vertical solids pressure substantially prevents pluggage or particulate bridging.
The surface configuration of the interior generally vertical wall of the upright cylindrical vessel according to the invention is preferably provided by means defining a surface configuration which comprises a plurality of right circular cone frustrums having a larger diameter at higher portions thereof than at lower portions thereof. Each of the cone frustrums may make an angle with respect to the vertical of about 10.degree.-30.degree. , and the cone frustrums can be discontinuous along the interior vertical wall, being spaced from each other a significant distance, or they may be provided in sequence, one immediately adjacent the other, without significant spacing between them. Where the vessel has a diameter of about 15-20 feet (adjacent the bottom thereof adjacent a particulate material discharge is located), the frustrums are positioned so that the bottom terminations thereof are vertically spaced from each other a distance S, in feet, determined according to the formula S=6.83-0.26 (D-15), where D is the bottom diameter of the vessel in feet. Also, under such circumstances the uppermost of the cone frustrums is not more than about 1.5 S from the top level of particulates in the vessel.
Where the vessel is a chip bin, a vibrating discharge is provided at the bottom, and there are also provided means for adding steam to the vessel. Steam may be added to the vessel at the vibratory discharge, as is conventional, and also may be added at one or more of the cone frustrum bottom terminations.
The cone frustrums may be solid concrete and define both the exterior and interior of the vessel, or they may be concrete disposed within a steel shell which surrounds them and provides the exterior of the vessel. Alternatively, the vessel may be a steel cylinder, and the cone frustrums may be metal plate connected to the interior generally vertical wall with portions thereof spaced from the wall (with steam addition at those portions of desired).
According to another aspect of the present invention, a method of constructing a generally upright vessel using a slip form which forms a right circular cone frustrum interior surface, is provided. The method comprises the steps of substantially sequentially: (a) Mounting a hopper at substantially the lowermost portion of the vessel. (b) Placing the slip form above the hopper. (c) Pouring concrete utilizing the slip form to form a first generally cylindrical wall segment above the hopper, and defining a right circular cone frustrum interior surface. (d) After the concrete poured in step (c) has hardened, moving the slip form above the formed concrete generally cylindrical wall segment. (e) Repeating steps (c) and (d) until a vessel of the desired height has been constructed of generally cylindrical concrete wall segments. And (f) providing a top structure on the topmost generally cylindrical wall segment. There is also preferably the further step of providing a metal support ring beneath the slip form before pouring each of the right circular cone frustrums.
According to yet another aspect of the present invention, another method of constructing a generally upright vessel using at least one slip form is provided. This method comprises the following steps: (a) Providing a cylindrical steel shell with steel shelves. (b) Mounting a hopper interior of the steel shell at substantially the lowermost portion of the vessel. (c) Placing one or more slip forms above the steel shelves. (d) Pouring concrete utilizing the slip forms to form right circular cone frustrum interior surfaces within the steel shell at the steel shelves. And (e) providing a top structure on the topmost portion of the steel shell.
It is the primary object of the present invention to provide an upright generally cylindrical vessel for storing particulate material where there is a minimum chance of the particulates plugging or bridging due to compression, and to a method of constructing such a vessel. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.